I hate the keybord shortcut for sending a message when it resembles
typing the dollar sign on my keyboard.... :-(
Please ignore my previous message on this subject, as it was unfinished.
This is a complete version....

Hi, all!

I'm flying model helicopters (not so much lately, but...) with
a conventional gyro. (Mechanical, that is)

I have seen and read about the so called "solid state" gyros that
has been on the market for some years now.

I've read that they all use the "Gyrostar ENC" sensors from MuRata.
(This may or may not be true, but at least some manufacturers use this
sensor, else it would probably not have been mentioned)

These gyros are usually very expensive. (more than
twice the price of a conventional one here in Norway)

And now I'm getting to the point.

It seems to me that making such a gyro should be possible
with a PIC and some external circuitry.

The sensor itself is not so expensive (approx 25 dollars) and I believe that
the other components needed besides the PIC will cost approximately
the same (an op amp, probably quad, and an A/D plus some discretes and
probably a temp sensor to compensate drift).

The inputs from the receiver and the outputs to the servo can be connected
directly to the PIC since the signal levels are TTL compatible.

I believe there are other R/C people on this list (at least one of the Andys).

I don't have the time for writing code, but if you point me to data on the optic
al
gyro concept or whatever it is, I can contribute to the hardware portion of the
design. Sounds too cool.

Chris Eddy
Pioneer Microsystems, Inc.

Oyvind Kaurstad wrote:

> The sensor itself is not so expensive (approx 25 dollars) and I believe that
> the other components needed besides the PIC will cost approximately
> the same (an op amp, probably quad, and an A/D plus some discretes and
> probably a temp sensor to compensate drift).
>

I'd toyed around with the idea of creating a piezo gyro also. This was
almost a year ago, Murata was not willing to give me 1 or 2 sensors, so I
bought one of those gyro mice and stripped the sensor from that, I ran into
problems with thermal drift and overall sensor stability and gave up on the
design.

I'll try to dig up the old code that I had. Maybe we can revive this
project

I have been trying to find a source for these sensors, but so far as I know,
Murata only sells the ENC gyros thru sales representatives. And the price
is $80 each in lots of less than 100. Where did you get the $25 each price?
Was that a price for new or used gyroes?

At $80 each, it may well be less expensive to buy products that contain the
gyros and dismantle them just for the gyros.

>I'd toyed around with the idea of creating a piezo gyro also. This was
>almost a year ago, Murata was not willing to give me 1 or 2 sensors, so I
>bought one of those gyro mice and stripped the sensor from that, I ran into
>problems with thermal drift and overall sensor stability and gave up on the
>design.

>I'll try to dig up the old code that I had. Maybe we can revive this
>project

Interesting.

Did you actually fly a model helicopter with your gyro?
It would be interesting to see your design.

>I have been trying to find a source for these sensors, but so far as I know,
>Murata only sells the ENC gyros thru sales representatives. And the price
>is $80 each in lots of less than 100. Where did you get the $25 each price?
>Was that a price for new or used gyroes?

Well. I lied a bit.
The Norwegian distributor I spoke with has a price of $27 in 10's, and down to
$17 in 100's. And they are new, of course.

I didn't care to convert the prices into dollars, so I just took an in-between
estimate
in my head. I missed the 10's price with a couple of dollars.

>At $80 each, it may well be less expensive to buy products that contain the
>gyros and dismantle them just for the gyros.

That's true.
I'm getting a sample or two in the near future from a company that uses these
things
in a product. Seems they've done a design error, and had to throw away quite
many
of these sensors, although the sensors are within spec. They just didn't read
the spec
very carefully when they did the design...

>I believe there are other R/C people on this list (at least one of the
Andys).
>
>What do you think? Doable or not?

Very do-able. No external ADC required - use the PIC16C73 or 76. Use
PORTB change to measure servo width. Use one CCP pin to send output to
servo. You only really need to have good conditioning on the ADC, or you
can convert the voltage to a PWM (like the ADXL02 does).

At 05:40 PM 9/21/98 -0700, you wrote:
>I have been trying to find a source for these sensors, but so far as I know,
>Murata only sells the ENC gyros thru sales representatives. And the price
>is $80 each in lots of less than 100. Where did you get the $25 each price?
>Was that a price for new or used gyroes?
>
>At $80 each, it may well be less expensive to buy products that contain the
>gyros and dismantle them just for the gyros.
>
>{Original Message removed}

At 06:31 AM 9/22/98 -0700, you wrote:
>Since the Murata gyros are outrageously priced, has anyone tried a Gyration
>MG 100 gyro? It's a two-axis piezoelectric unit, and conceivably could be
>had at a lesser cost.

>I got them $15 each from (I think) FAI.
>
>Andy
>
>
>At 05:40 PM 9/21/98 -0700, you wrote:
>>I have been trying to find a source for these sensors, but so far as I
know,
>>Murata only sells the ENC gyros thru sales representatives. And the price
>>is $80 each in lots of less than 100. Where did you get the $25 each
price?
>>Was that a price for new or used gyroes?
>>
>>At $80 each, it may well be less expensive to buy products that contain
the{Quote hidden}

>>gyros and dismantle them just for the gyros.
>>
>>-----Original Message-----
>>From: Oyvind Kaurstad <.....oyvind.kaurstadKILLspam.....NOFAC.ABB.NO>
>>To: EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU <PICLISTspam_OUTMITVMA.MIT.EDU>
>>Date: Monday, September 21, 1998 7:11 AM
>>Subject: Model heli gyros.
>>
>>
>>I hate the keybord shortcut for sending a message when it resembles
>>typing the dollar sign on my keyboard.... :-(
>>Please ignore my previous message on this subject, as it was unfinished.
>>This is a complete version....
>>
>>
>>Hi, all!
>>
>>I'm flying model helicopters (not so much lately, but...) with
>>a conventional gyro. (Mechanical, that is)
>>
>>I have seen and read about the so called "solid state" gyros that
>>has been on the market for some years now.
>>
>>I've read that they all use the "Gyrostar ENC" sensors from MuRata.
>>(This may or may not be true, but at least some manufacturers use this
>>sensor, else it would probably not have been mentioned)
>>
>>These gyros are usually very expensive. (more than
>>twice the price of a conventional one here in Norway)
>>
>>And now I'm getting to the point.
>>
>>It seems to me that making such a gyro should be possible
>>with a PIC and some external circuitry.
>>
>>The sensor itself is not so expensive (approx 25 dollars) and I believe

>>the other components needed besides the PIC will cost approximately
>>the same (an op amp, probably quad, and an A/D plus some discretes and
>>probably a temp sensor to compensate drift).
>>
>>The inputs from the receiver and the outputs to the servo can be connected
>>directly to the PIC since the signal levels are TTL compatible.
>>
>>I believe there are other R/C people on this list (at least one of the
>>Andys).
>>
>>What do you think? Doable or not?
>>
>>-Oyvind
>>
>>
>==================================================================
>Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
>==================================================================
>

FYI Jameco sells a miniature flux gate compass that has 2 axis resolution
of about 2 degrees and could be substituted for a gyrostar. The interface
is digital (SPI or such) and this has the advantage of magnetically
accurate flying ;)

> I'd toyed around with the idea of creating a piezo gyro also. This was
> almost a year ago, Murata was not willing to give me 1 or 2 sensors, so I
> bought one of those gyro mice and stripped the sensor from that, I ran into
> problems with thermal drift and overall sensor stability and gave up on the
> design.

The accelerometer mice and the gyrostars are 2 different things. The
gyrostars have an offset and do not drift. Their gain changes somewhat
with temperature but a heli tail rotor gyro is not so sensitive to that.

There was someone on the list selling gyro assemblies from camera image
stabilizers. Each of these contains 2 gyrostars. Maybe he will re-post his
offer now.

> These gyros are usually very expensive. (more than
> twice the price of a conventional one here in Norway)

so someone is trying to rip you off... they are CHEAPER actually, they
were expensive when they were a novelty. You should not pay more than $110
for a one-axis one, complete sealed in the box with warranty, and this is
the high side price.

I'll never understand why a mechanical contraption with a whole collection
of closely toleranced moving parts can be sold for less money than the
equivalent solid state design, once the novelty stage passes.

> The sensor itself is not so expensive (approx 25 dollars) and I believe that
> the other components needed besides the PIC will cost approximately
> the same (an op amp, probably quad, and an A/D plus some discretes and
> probably a temp sensor to compensate drift).

No drift or temperature compensator is required, the gyrostars are rate
gyros. The A/D can be inside the PIC. If you do not have gyro
horizon/compass requirements then a 12C671 and a CA3260 or such are all
the hardware needed. When I investigated this, I used a 16C71 and LM324.
The 324's performance could be improved on (thus the 3260).

The nice thing is, these gyros require so little power and weigh so little
that they can be used with electric helis.

> The inputs from the receiver and the outputs to the servo can be connected
> directly to the PIC since the signal levels are TTL compatible.

Yes. You can even make the chopper turn slowly if the radio signal is
lost... which is a very good idea in view of the price of the bird imho.

> What do you think? Doable or not?

Doable, but there will be a reasonable amount of effort required to get
the low-pass filter and the digital integrator deadband right. Gyrostars
have an offset that varies fom unit to unit and this must be allowed for.
A trimmer is not a good idea an a heli but a 93c46 could be.

>>I believe there are other R/C people on this list (at least one of the
>Andys).
>>
>>What do you think? Doable or not?

>Very do-able. No external ADC required - use the PIC16C73 or 76. Use
>PORTB change to measure servo width. Use one CCP pin to send output to
>servo. You only really need to have good conditioning on the ADC, or you
>can convert the voltage to a PWM (like the ADXL02 does).

Well, I was thinking of using the F84 and bit-bang the whole thing, and I was
planning on using an external ADC (MAX 187). Mostly because I have a couple
of those in my drawer, and I also have the routines to read it.

It's 12 bits, and that may be a bit over the top, but it's easy to scale
down in software if necessary.

>> I'd toyed around with the idea of creating a piezo gyro also. This was
>> almost a year ago, Murata was not willing to give me 1 or 2 sensors, so I
>> bought one of those gyro mice and stripped the sensor from that, I ran into
>> problems with thermal drift and overall sensor stability and gave up on the
>> design.

>The accelerometer mice and the gyrostars are 2 different things. The
>gyrostars have an offset and do not drift. Their gain changes somewhat
>with temperature but a heli tail rotor gyro is not so sensitive to that.

So, you're saying that at zero rotation the output is constant over the complete
temperature range?

Does anyone have (or know where to find) a complete datasheet for the gyrostars?
I have checked the Murata website, but they only have a stripped HTML thingy.
Surely there must be a complete datasheet somewhere, preferrably in pdf-format.

I hate the keybord shortcut for sending a message when it resemblestyping the dollar sign on my keyboard.... :-(Please ignore my previous message on this subject, as it was unfinished.This is a complete version....

I have seen and read about the so called "solid state" gyros thathas been on the market for some years now.

I've read that they all use the "Gyrostar ENC" sensors from MuRata.(This may or may not be true, but at least some manufacturers use thissensor, else it would probably not have been mentioned)

These gyros are usually very expensive. (more than twice the price of a conventional one here in Norway)

And now I'm getting to the point.

It seems to me that making such a gyro should be possiblewith a PIC and some external circuitry.

The sensor itself is not so expensive (approx 25 dollars) and I believe thatthe other components needed besides the PIC will cost approximatelythe same (an op amp, probably quad, and an A/D plus some discretes andprobably a temp sensor to compensate drift).

The inputs from the receiver and the outputs to the servo can be connecteddirectly to the PIC since the signal levels are TTL compatible.

I believe there are other R/C people on this list (at least one of the Andys).

>> I've read that they all use the "Gyrostar ENC" sensors from MuRata.

>mostly correct, all others seem to be copies thereof...

Close enough....

>> These gyros are usually very expensive. (more than
>> twice the price of a conventional one here in Norway)

>so someone is trying to rip you off... they are CHEAPER actually, they
>were expensive when they were a novelty. You should not pay more than $110
>for a one-axis one, complete sealed in the box with warranty, and this is
>the high side price.

I suppose the marketing guys have a certain influence here...

"If it is better we can charge more for it, it doesn't matter if it is cheaper
to manufacture. We will make more money that way..."

>I'll never understand why a mechanical contraption with a whole collection
>of closely toleranced moving parts can be sold for less money than the
>equivalent solid state design, once the novelty stage passes.

>> The sensor itself is not so expensive (approx 25 dollars) and I believe that
>> the other components needed besides the PIC will cost approximately
>> the same (an op amp, probably quad, and an A/D plus some discretes and
>> probably a temp sensor to compensate drift).

>No drift or temperature compensator is required, the gyrostars are rate
>gyros. The A/D can be inside the PIC. If you do not have gyro
>horizon/compass requirements then a 12C671 and a CA3260 or such are all
>the hardware needed. When I investigated this, I used a 16C71 and LM324.
>The 324's performance could be improved on (thus the 3260).

I assume there are lots of other opamps that could be used, also.
But it should be low-noise, low power types, I suppose.

I'm not sure of how much resolution I will need on the ADC, and I'm not
sure how to do the mixing with the incoming signal from the receiver.
Does it sound ok to kind of overlay the gyro signal on the receiver signal?
With adjustable gain, of course.

I saw an example amplifier circuit on the Murata website, but they used both
a highpass and a lowpass filter on the signal, thus eliminating the DC
component.
In the case of a model heli gyro this will be undesirable, I think.
If I do that I will not be able to detect if the helicopter is continuosly
pirouetting, for
instance.

>The nice thing is, these gyros require so little power and weigh so little
>that they can be used with electric helis.

I'm not into electric helis, but obviously this is a great asset.

>> The inputs from the receiver and the outputs to the servo can be connected
>> directly to the PIC since the signal levels are TTL compatible.

>Yes. You can even make the chopper turn slowly if the radio signal is
>lost... which is a very good idea in view of the price of the bird imho.

But how would you determine for how long it should turn?

>> What do you think? Doable or not?

>Doable, but there will be a reasonable amount of effort required to get
>the low-pass filter and the digital integrator deadband right. Gyrostars
>have an offset that varies fom unit to unit and this must be allowed for.
>A trimmer is not a good idea an a heli but a 93c46 could be.

What about an initial zero read routine in the gyro software?
It would of course have to assume that the heli is not rotating when it is first
powered, but that is usually the case, so....

Why would you want to integrate the signal?
Isn't this kind of a closed-loop thing? You apply opposite tail rotor until the
rotation stops? (Or until a preset deadband is reached)

> I'd toyed around with the idea of creating a piezo gyro also. This was
> almost a year ago, Murata was not willing to give me 1 or 2 sensors, so I
> bought one of those gyro mice and stripped the sensor from that, I ran into
> problems with thermal drift and overall sensor stability and gave up on the
> design.

The accelerometer mice and the gyrostars are 2 different things. The
gyrostars have an offset and do not drift. Their gain changes somewhat
with temperature but a heli tail rotor gyro is not so sensitive to that.

There was someone on the list selling gyro assemblies from camera image
stabilizers. Each of these contains 2 gyrostars. Maybe he will re-post his
offer now.

> >The 324's performance could be improved on (thus the 3260).
>
> I assume there are lots of other opamps that could be used, also.
> But it should be low-noise, low power types, I suppose.

You need sufficient GBW at 50 kHz to get rid of a certain residual signal
from the sensor. You will see.

> I'm not sure of how much resolution I will need on the ADC, and I'm not

Sensor output ~= 0.3..0.8 mV / (degree * second)

> sure how to do the mixing with the incoming signal from the receiver.
> Does it sound ok to kind of overlay the gyro signal on the receiver signal?
> With adjustable gain, of course.

Oh ! I had thought that you'd done this before... (interfacing to PWM
RC servo circuits). You need to do some reading here. Mixing with the
signal is DEFINITELY not the way to go.

Also, there are some implications to make a closed loop servo (hint: the
stability of a loop with gain and respectable delays and dead-bands built
in).

> I saw an example amplifier circuit on the Murata website, but they used both
> a highpass and a lowpass filter on the signal, thus eliminating the DC
> component.

Look again, I am quite sure that the DC component is not eliminated unless
the circuit is meant to do that (i.e. rate of rate gyro == rpm
stabilizer).

> >Yes. You can even make the chopper turn slowly if the radio signal is
> >lost... which is a very good idea in view of the price of the bird imho.
>
> But how would you determine for how long it should turn?

Until the ground stops it or radio liaison is re-established, whichever
happens first... ;) This assumes that the heli knows how to auto-rotate
w/o help (ok, skip the flare, use a shovel instead, but it's still
better than a *sieve* and *magnifiying glass*).

> What about an initial zero read routine in the gyro software? It would
> of course have to assume that the heli is not rotating when it is first
> powered, but that is usually the case, so....

You can do that.

> Why would you want to integrate the signal? Isn't this kind of a
> closed-loop thing? You apply opposite tail rotor until the rotation
> stops? (Or until a preset deadband is reached)

I was thinking of a safety feature here. If the total degrees over a
certain time is too large, assume that the sensor died and turn off servo
loop.

> >The accelerometer mice and the gyrostars are 2 different things. The
> >gyrostars have an offset and do not drift. Their gain changes somewhat
> >with temperature but a heli tail rotor gyro is not so sensitive to that.
>
> So, you're saying that at zero rotation the output is constant over the
> complete temperature range?

I suppose that if it gets very cold then condensation can be a problem,
although the can is sealed almost hermetically.

The output of a gyrostar is inherently derived from a differential (i.e.
balanced) quantity (although the O/P is not differential but referenced
to an external bias you supply) so any internal drift should cancel out.

> Does anyone have (or know where to find) a complete datasheet for the
> gyrostars? I have checked the Murata website, but they only have a
> stripped HTML thingy. Surely there must be a complete datasheet
> somewhere, preferrably in pdf-format.

I got what I was given and worked out the missing details using a test
circuit strapped to a pendulum ;) Actually, I think I've invented a way to
calibrate the thing completely without needing human involvement.

>> >The 324's performance could be improved on (thus the 3260).
>>
>> I assume there are lots of other opamps that could be used, also.
>> But it should be low-noise, low power types, I suppose.

>You need sufficient GBW at 50 kHz to get rid of a certain residual signal
>from the sensor. You will see.

I suppose the sensor will have some noise at around 25 kHz, as that is the
resonance frequency of the sensor, but what is the 50 kHz you refer to?
Harmonics?

>> I'm not sure of how much resolution I will need on the ADC, and I'm not

>Sensor output ~= 0.3..0.8 mV / (degree * second)

Oh.
In the datasheet I've seen it says 1.11 mV/deg/sec.
That means if the rotational speed changes from zero to 1 degree per second
the sensor will change its output with 1.11 mV, right?

If I use the MAX 187, I will get 1 mV resolution over the range 0 to 4.096 V.
That should suffice....

>> sure how to do the mixing with the incoming signal from the receiver.
>> Does it sound ok to kind of overlay the gyro signal on the receiver signal?
>> With adjustable gain, of course.

>Oh ! I had thought that you'd done this before... (interfacing to PWM
>RC servo circuits). You need to do some reading here. Mixing with the
>signal is DEFINITELY not the way to go.

I have worked with R/C servos and PICs before. I once made a robot this way.
What I don't know is how to let both the gyro and the pilot have control over
the tail.

I'm not sure if you've misunderstood me a little, so I'll explain a bit better
what I had in mind.

The receiver will send a signal to the gyro. Lets say a 1.5 mS signal.
If we assume the heli is at zero rotation at this point and a gust of wind
tries to turn the heli, then the gyro will add an error correction signal
of for instance 0.2 mS to the receiver signal before sending it to the servo.

The amount of error correction will depend on both gyro gain and how fast
the heli is turned by the wind.

So, when I say mixing I mean adding and subtracting to the signal in the PIC,
not
analog mixing of the signals.

Does it still sound like I'm totally lost here?

>Also, there are some implications to make a closed loop servo (hint: the
>stability of a loop with gain and respectable delays and dead-bands built
>in).

Yes, but I suppose I will have to experiment a little with this...

>> I saw an example amplifier circuit on the Murata website, but they used both
>> a highpass and a lowpass filter on the signal, thus eliminating the DC
>> component.

>Look again, I am quite sure that the DC component is not eliminated unless
>the circuit is meant to do that (i.e. rate of rate gyro == rpm
>stabilizer).

I have no idea what it's meant to do, but since they use an RC highpass filter
immediately on the sensor output, the DC component is eliminated.
The filter has a cutoff frequency of approx. 0.3 Hz.

>> >Yes. You can even make the chopper turn slowly if the radio signal is
>> >lost... which is a very good idea in view of the price of the bird imho.
>>
>> But how would you determine for how long it should turn?

>Until the ground stops it or radio liaison is re-established, whichever
>happens first... ;) This assumes that the heli knows how to auto-rotate
>w/o help (ok, skip the flare, use a shovel instead, but it's still
>better than a *sieve* and *magnifiying glass*).

Have you seen a heli that's auto-rotating on its own?
And in an auto rotation most model helis will have the tail rotor disengaged
anyway, so the gyro has no control over things.

Some helis can be steered with the tail in an auto-rotaion, but if so, you would
definately not want to spend a lot of precious energy on pirouetting on
your way down.

>> What about an initial zero read routine in the gyro software? It would
>> of course have to assume that the heli is not rotating when it is first
>> powered, but that is usually the case, so....

>You can do that.

Then that's what I will do.

>> Why would you want to integrate the signal? Isn't this kind of a
>> closed-loop thing? You apply opposite tail rotor until the rotation
>> stops? (Or until a preset deadband is reached)

>I was thinking of a safety feature here. If the total degrees over a
>certain time is too large, assume that the sensor died and turn off servo
>loop.

Aha. That's not a bad idea, although it will have to have quite a long time
constant, since pirouetting is a very common thing to play with...

-Oyvind

P.S: I can take this discussion private, if people think it's a bandwidth waste.

>>Very simple to do. Arcamax unit is _exactly_ this.
>
>I have no knowledge of this unit.
>What company is behind it?
>
>Do they have a wb page?
>
>When you say _exactly_, do you mean they use a PIC as the brain?

Arcamax, Inc.

I reverse-engineered the Arcamax unit for FMA (they were selling the
Arcamax unit, and were being raped on price and quality was horrible).

I don't know about a web page, but they are known on the rec.models.rc.air
newsgroup - ask there.

Exactly means exactly. The Arcamax unit I disassembled was a
PIC16C73-based piece. It used some external parts to boost the incoming
voltage so that the PIC was guaranteed 5.0V. Still have the schematics
somewhere. As I recall they were Analog Devices and Linear Tech parts. No
EEPROM, a little temp compensation (in software).

Cute little device, actually, it's a shame that Arcamax's relationship with
FMA fell on as bad a situation as mine (and several others') did.

> >Sensor output ~= 0.3..0.8 mV / (degree * second)
>
> Oh.
> In the datasheet I've seen it says 1.11 mV/deg/sec.
> That means if the rotational speed changes from zero to 1 degree per second
> the sensor will change its output with 1.11 mV, right?

I measured each sensor I used in the final circuit. I have a limited trust
in translated datasheets ;( Also, my sensors were Tokin.

> If I use the MAX 187, I will get 1 mV resolution over the range 0 to 4.096 V.
> That should suffice....

a) Do you plan to accomodate turn rates of ~1845 deg/sec ? (about 300 rpm)
If not, amplify the signal somewhat and concentrate on accurate
directional stability imho (30-50 mV/deg at the AD input is more like
it. This will saturate the system at 40 degrees/sec or so. How fast do
you plan to turn ? ;).
b) Why not use a PIC A/D converter ? A 16C671 will do that, no ?

You have servo pulses coming into the PIC from the Rx. The PIC computes
the PID or fuzzy algorythm for the gyro and then adds or substracts a
value to the incoming pulse width, after which it generates a new pulse to
the servo with the new width.

> The amount of error correction will depend on both gyro gain and how fast
> the heli is turned by the wind.

Yes. But the wind is not the main factor imho, unless you fly between
buildings etc. with a lot of turbulence (which is illegal and dangerous
BTW).

> Does it still sound like I'm totally lost here?

No, but you are looking forward to an interesting few weeks/months.
Closed loop servo systems subjected to un-calculable perturbations from
the outside are fun to tune. All heli tail gyros have controls to be tuned
by the pilot as was said before, and this is not by accident. There is
also in-flight gain control sometimes.

I think that you should invest in one of those articulated strut heli
training stands when you check out the system on the bird.

> Yes, but I suppose I will have to experiment a little with this...

Better start with the theory. It took about 80 years for control theory to
reach the point where planes don't fall out of the sky, motors do not
explode by over-revving etc.

> I have no idea what it's meant to do, but since they use an RC highpass filter
> immediately on the sensor output, the DC component is eliminated.
> The filter has a cutoff frequency of approx. 0.3 Hz.

> >> >Yes. You can even make the chopper turn slowly if the radio signal is
> >> >lost... which is a very good idea in view of the price of the bird imho.
> >>
> >> But how would you determine for how long it should turn?
>
> >Until the ground stops it or radio liaison is re-established, whichever
> >happens first... ;) This assumes that the heli knows how to auto-rotate
> >w/o help (ok, skip the flare, use a shovel instead, but it's still
> >better than a *sieve* and *magnifiying glass*).
>
> Have you seen a heli that's auto-rotating on its own?

Most sane heli radios I've seen (not many, this is not my hobby) are set
up to select dead center stick, idle engine and very slightly down (?)
collective if radio signal is lost. Am I missing something ? This is not
auto-rotation in the proper sense of the word but it is better than flying
clothes iron style landings. If the coning angle is reasonable then the
bird should fall on the struts at less than 6 m/sec. Thus you can use the
shovel to recover the more expensive parts, as opposed to the magnifying
glass & sieve if it hits real hard...

> And in an auto rotation most model helis will have the tail rotor disengaged
> anyway, so the gyro has no control over things.

I forgot about that. Does the Heim mechanism disconnect the tail with the
centrifugal clutch ?

> Aha. That's not a bad idea, although it will have to have quite a long time
> constant, since pirouetting is a very common thing to play with...

Hmm. If you pirouette so much, why do you need a tail rotor <g> ?

Andy Kunz said that the integration can be used for directional control.
I'd say that it can be used, but with great caution. This type of sensor
drifts a lot and it cannot really be relied on for direction control. A
compass module from Jameco will do this much better imho. It would also be
illegal to use it for this in some countries.

>Andy Kunz said that the integration can be used for directional control.
>I'd say that it can be used, but with great caution. This type of sensor
>drifts a lot and it cannot really be relied on for direction control. A
>compass module from Jameco will do this much better imho. It would also be
>illegal to use it for this in some countries.

Actually, the drift over a 15-minute flight (typical) is very little,
especially if the pilot has taken the recommended precautions of putting
the bird out on the flight line to get the temps up. He'd have a pretty
tough time flying it if he pulled it out of his air-conditioned car and
flew over a hot black runway, surely, but otherwise they are adequately
stable.

Many countries discourage dissemination of technologies
thought to have military or para-military significance.
This is said to be the case with MIR in the US, for
instance. Governments being what they are, there is'nt much
sense or consistency in the application of such restrictions,
overt or otherwise.
For example, as recently mentioned by someone on the list,
piezo gyros vs. capacitive accelerometers. Or the encryption
algorithm silliness. Go figure.

At 12:32 PM 9/24/98 -0700, you wrote:
>Andy Kunz wrote:
>
>> 3) Why would it NOT be legal?
>
>Many countries discourage dissemination of technologies
>thought to have military or para-military significance.
>This is said to be the case with MIR in the US, for
>instance. Governments being what they are, there is'nt much

Please excuse my ignorance, what is MIR in this case? Surely, it is not the
Russian Space Station?!

Peter L. Peres wrote:
> it. This will saturate the system at 40 degrees/sec or so. How fast do
> you plan to turn ? ;).

I was going to mention that you can turn at great rates, a
540deg stall turn is done in a second or so, but you don't
want the gyro fighting you. But there are other reasons to
need the gyro working at high deflection. Mentioned below..

> Yes. But the wind is not the main factor imho, unless you fly between
> buildings etc. with a lot of turbulence (which is illegal and dangerous

Wind is relative. Flying tail first and sideways loops will
have tremendous relative winds to the tail rotor. 35 MPH +

> No, but you are looking forward to an interesting few weeks/months.
> Closed loop servo systems subjected to un-calculable perturbations from
> the outside are fun to tune. All heli tail gyros have controls to be tuned
> by the pilot as was said before, and this is not by accident. There is
> also in-flight gain control sometimes.

No kidding here. If he was expecting this to be worthwhile
in even medium quantity vs just buying one at $200-300 he
will have to value his time at $.02 an hour.

> Andy Kunz said that the integration can be used for directional control.
> I'd say that it can be used, but with great caution. This type of sensor
> drifts a lot and it cannot really be relied on for direction control.

I doubt a compass will work here, since it won't know what's
going on with the attitude of the heli. I can just see
someone doing a loop and it flipping tail first when upside
down to keep the nose pointed north or something since no
tail rotor was put in but the earth's poles flipped. The
heading lock piezo gyros are excellent, so I would assume
the integration can be done and work well. Only problem is
it will probably take them 5 years to get things up to the
quality of what's out now..

>>>Very simple to do. Arcamax unit is _exactly_ this.
>>
>>I have no knowledge of this unit.
>>What company is behind it?
>>
>>Do they have a wb page?
>>
>>When you say _exactly_, do you mean they use a PIC as the brain?

>Arcamax, Inc.

>I reverse-engineered the Arcamax unit for FMA (they were selling the
>Arcamax unit, and were being raped on price and quality was horrible).

What is FMA?
Flying Models Assosiation? :-)

>I don't know about a web page, but they are known on the rec.models.rc.air
>newsgroup - ask there.

They seem to have four different gyro systems available at reasonable prices.
Which one did you reverse-engineer?

>Exactly means exactly. The Arcamax unit I disassembled was a
>PIC16C73-based piece. It used some external parts to boost the incoming
>voltage so that the PIC was guaranteed 5.0V. Still have the schematics
>somewhere. As I recall they were Analog Devices and Linear Tech parts. No
>EEPROM, a little temp compensation (in software).

Are you allowed to share the schematics?

>Cute little device, actually, it's a shame that Arcamax's relationship with
>FMA fell on as bad a situation as mine (and several others') did.

I have no knowledge of FMA, but since I live in Norway I don't think it
matters...

>If not, amplify the signal somewhat and concentrate on accurate
>directional stability imho (30-50 mV/deg at the AD input is more like
>it. This will saturate the system at 40 degrees/sec or so. How fast do
>you plan to turn ? ;).

Faster. :-)

>b) Why not use a PIC A/D converter ? A 16C671 will do that, no ?

Undoubtedly.
It's just that I don't have any 16C671, and if I had, it wouldn't help since I
don't
have a programmer to program it. I don't have an UV eraser either.

What I do have is F84's and MAX187's.... So that's why.

>You have servo pulses coming into the PIC from the Rx. The PIC computes
>the PID or fuzzy algorythm for the gyro and then adds or substracts a
>value to the incoming pulse width, after which it generates a new pulse to
>the servo with the new width.

Exactly.

>> The amount of error correction will depend on both gyro gain and how fast
>> the heli is turned by the wind.

>Yes. But the wind is not the main factor imho, unless you fly between
>buildings etc. with a lot of turbulence (which is illegal and dangerous
>BTW).

I do not fly in between buildings, but I do fly in crosswind, for instance..
.

>> Does it still sound like I'm totally lost here?

>No, but you are looking forward to an interesting few weeks/months.
>Closed loop servo systems subjected to un-calculable perturbations from
>the outside are fun to tune. All heli tail gyros have controls to be tuned
>by the pilot as was said before, and this is not by accident. There is
>also in-flight gain control sometimes.

My present gyro system has in-flight gain control.

>I think that you should invest in one of those articulated strut heli
>training stands when you check out the system on the bird.

The testing will be the worst part... It's expensive to do mistakes
in this business....

>> Yes, but I suppose I will have to experiment a little with this...

>Better start with the theory. It took about 80 years for control theory to
>reach the point where planes don't fall out of the sky, motors do not
>explode by over-revving etc.

Of course.
But experimenting will also be a necessity.

>> I have no idea what it's meant to do, but since they use an RC highpass
>filter
>> immediately on the sensor output, the DC component is eliminated.
>> The filter has a cutoff frequency of approx. 0.3 Hz.

>> >> >Yes. You can even make the chopper turn slowly if the radio signal is
>> >> >lost... which is a very good idea in view of the price of the bird imho.
>> >>
>> >> But how would you determine for how long it should turn?
>>
>> >Until the ground stops it or radio liaison is re-established, whichever
>> >happens first... ;) This assumes that the heli knows how to auto-rotate
>> >w/o help (ok, skip the flare, use a shovel instead, but it's still
>> >better than a *sieve* and *magnifiying glass*).
>>
>> Have you seen a heli that's auto-rotating on its own?

>Most sane heli radios I've seen (not many, this is not my hobby) are set
>up to select dead center stick, idle engine and very slightly down (?)
>collective if radio signal is lost. Am I missing something ? This is not
>auto-rotation in the proper sense of the word but it is better than flying
>clothes iron style landings. If the coning angle is reasonable then the
>bird should fall on the struts at less than 6 m/sec. Thus you can use the
>shovel to recover the more expensive parts, as opposed to the magnifying
>glass & sieve if it hits real hard...

This feature is called "Fail-safe" and it is more useful on planes than
on helicopters, imho.

>> And in an auto rotation most model helis will have the tail rotor disengaged
>> anyway, so the gyro has no control over things.

>I forgot about that. Does the Heim mechanism disconnect the tail with the
>centrifugal clutch ?

I'm not sure, but that's the way it's usually done.

>> Aha. That's not a bad idea, although it will have to have quite a long time
>> constant, since pirouetting is a very common thing to play with...

>Hmm. If you pirouette so much, why do you need a tail rotor <g> ?

:-)

>Andy Kunz said that the integration can be used for directional control.
>I'd say that it can be used, but with great caution. This type of sensor
>drifts a lot and it cannot really be relied on for direction control. A
>compass module from Jameco will do this much better imho. It would also be
>illegal to use it for this in some countries.

But time is a factor here.
If you plan to fly with the same heading for hours then you will get into
trouble, but
for shorter periods of time it will not drift that much. At least not if it is
temperature
compensated.

>> it. This will saturate the system at 40 degrees/sec or so. How fast do
>> you plan to turn ? ;).

> I was going to mention that you can turn at great rates, a
>540deg stall turn is done in a second or so, but you don't
>want the gyro fighting you. But there are other reasons to
>need the gyro working at high deflection. Mentioned below..

But there is a solution to this.
The CSM gyro has solved this problem by making it a "yaw rate demand"
gyro. The stick input reflects the yaw rate that the pilot wishes, and not
the deflection of the tail rotor blades. (Not directly, anyway)

This is clever, I think. The gyro will not "fight" the control input from the
pilot, like in a conventional system.

>> Yes. But the wind is not the main factor imho, unless you fly between
>> buildings etc. with a lot of turbulence (which is illegal and dangerous

>> No, but you are looking forward to an interesting few weeks/months.
>> Closed loop servo systems subjected to un-calculable perturbations from
>> the outside are fun to tune. All heli tail gyros have controls to be tuned
>> by the pilot as was said before, and this is not by accident. There is
>> also in-flight gain control sometimes.

>No kidding here. If he was expecting this to be worthwhile
>in even medium quantity vs just buying one at $200-300 he
>will have to value his time at $.02 an hour.

I'm not expecting to make money on this.
It's pure fun. I just want to see if I'm able to make a working system.
This is not job related at all, I'm going to do this in my spare time.

>I reverse-engineered the Arcamax unit for FMA (they were selling the
>Arcamax unit, and were being raped on price and quality was horrible).
>
>I don't know about a web page, but they are known on the rec.models.rc.air
>newsgroup - ask there.
>
>Exactly means exactly. The Arcamax unit I disassembled was a
>PIC16C73-based piece. It used some external parts to boost the incoming
>voltage so that the PIC was guaranteed 5.0V. Still have the schematics
>somewhere. As I recall they were Analog Devices and Linear Tech parts. No
>EEPROM, a little temp compensation (in software).
>
>Cute little device, actually, it's a shame that Arcamax's relationship with
>FMA fell on as bad a situation as mine (and several others') did.
Can you send me this schematic and source ?
Thanks in advance !

>Exactly means exactly. The Arcamax unit I disassembled was a
>PIC16C73-based piece. It used some external parts to boost the incoming
>voltage so that the PIC was guaranteed 5.0V. Still have the schematics
>somewhere. As I recall they were Analog Devices and Linear Tech parts. No
>EEPROM, a little temp compensation (in software).
What AD parts used ?

At 18:55 24.9.1998 +0000, you wrote:
> have you seen and/or used the miniature flux gate compass sold by Jameco
>for heli/model directional and heading control ? Have you considered it
>for this ? (and is it legal in your country ? <g>).
>

I have two of those toys (Vector 2X or something.., the gimbaled ones). I
am affraid that the whole thing is too weak to withstand the vibrations in
any RC model, especially in heli. On the other side, I tried one compass
with success in RC car.

> Andy Kunz wrote:
>
> > 3) Why would it NOT be legal?
>
> Many countries discourage dissemination of technologies
> thought to have military or para-military significance.
> This is said to be the case with MIR in the US, for
> instance. Governments being what they are, there is'nt much
> sense or consistency in the application of such restrictions,
> overt or otherwise.

imho, seen from outside the US and EU, this has 3 effects:

1. It flags all technology useable by bad guys reliably, and gives them
good starting points on where and what to search for (illegally). F. ex.
the Waasenaar treaty lists, which is in the public domain, is actually a
shopping list for anyone out to do bad things with technology.

2. It generates a clear division between foreign companies who would
legitimately use the technology in products, with good intentions (ex:
e-commerce), and inland companies who loose business and money invested in
research projects and patent defenses etc.

3. It is an un-enforceable system, as most exports of crypto stuff 'in
printed form' from the US have shown. See PGP etc.

> Peter L. Peres wrote:
> > it. This will saturate the system at 40 degrees/sec or so. How fast do
> > you plan to turn ? ;).
>
> I was going to mention that you can turn at great rates, a
> 540deg stall turn is done in a second or so, but you don't

All I can say about this is, that my favorite description of a helicopter
(not necessarily a model) is: "1000 moving parts continuously trying to
destroy each other" (or words to that effect). This is used as a .sig by a
pilot in a USENET news group, no less.

> I doubt a compass will work here, since it won't know what's
> going on with the attitude of the heli. I can just see
> someone doing a loop and it flipping tail first when upside
> down to keep the nose pointed north or something since no
> tail rotor was put in but the earth's poles flipped. The

I understand that in normal aircraft that do not have an integrated
attitude sensor system the compass is not worth much when the vehicle is
off horizontal by more than 30-45 degrees, in despite of gymbals and
ball-style compasses. This, and magnetic deviation, were the reasons for
the widespread use of gyro compasses since before WW2.

And the full answer is, that an un-gymballed compass can be used to keep
magnetic heading in combination with an attitude sensor (which has to be
gyro or inertial) that can tell when it is in good reading range. An ARDF
system is much easier to implement at the present stage of things imho ;)

> The CSM gyro has solved this problem by making it a "yaw rate demand"
> gyro. The stick input reflects the yaw rate that the pilot wishes, and not
> the deflection of the tail rotor blades. (Not directly, anyway)
>
> This is clever, I think. The gyro will not "fight" the control input from the
> pilot, like in a conventional system.

I think that most flying things are moving to rate demand control, with
the introduction of closed-loop fly by wire. This is much more intuitive
than the usual human-controlled 'PID' that takes years to learn ;)

> It's pure fun. I just want to see if I'm able to make a working system.
> This is not job related at all, I'm going to do this in my spare time.

> >I have little experience with this. I had a horrible lecturer in this subject
> >at school... Bad excuse, I know... -)
>
> Fuzzy logic would work just as well, maybe better.

Certainly, but unless he is good at fuzzy logic system tuning he is much
more likely to produce a system with hidden ugly bugs than with PID. I
have mentioned servo play in a previous posting in this context, PID is
fooled by this, fuzzy can do.

> P.S. Why it should not be legal to put compass,GPS,IR tracking device or
> anything else into RC heli ?

The last time I checked, adding auto-pilot features to any mobile such
that it can navigate without human countrol makes it illegal as a model.
There is also a weight limit for models that can be flown in most
countries (USA == 5 kg ?).

If you read between the lines, a small RC aircraft or boat can be turned
easily into a torpedo or cruise missile, with 1-4 kg of explosive on
board. You DON'T want college kids playing with that, nor anything like
this available off the shelf to be bought by your next door revolutionary
cell techie.

At the present stage of things, it works out like this: better technology
and systems are protected from public access by an IQ barrier, in the
sense that you need to understand the technology in order to be able to
use it. Look for example at good computing technology: you have to
understand Unix to be able to use them. Otherwise you are stuck with GPFs
and limited choice menus (but with rewarding animations) <g>.

At 06:04 PM 9/25/98 +0000, you wrote:
>The last time I checked, adding auto-pilot features to any mobile such
>that it can navigate without human countrol makes it illegal as a model.
>There is also a weight limit for models that can be flown in most
>countries (USA == 5 kg ?).
>

Models MUCH larger than 5kg are routinely flown. 1/3 and 1/4 scale models
of large aricraft are sometimes as big and almost as heavy as full size
light aircraft. I am not really sure of the regulations, but models above 5
kg are very common.

>The last time I checked, adding auto-pilot features to any mobile such
>that it can navigate without human countrol makes it illegal as a model.
>There is also a weight limit for models that can be flown in most
>countries (USA == 5 kg ?).

Israel exports model auto-pilot systems for hobby use in the USA (see Hobby
Lobby online). Many autonomous robots are built here for experimental
non-military use. We regularly fly models over 5Kg here, also. 5Kg is a
typical model weight (11 pounds or so).

OK Folks,
So which one of the you guys is going to step forward to provide the fuzzy
logic tutorial. I would love to try and get to grips with this maybe we
could use this heli control system as an example.....

Or at least maybe those in the know could provide a few good pointers to
books/articles/Web pages etc.

Thanks

Andy

>> Fuzzy logic would work just as well, maybe better.
>
>Certainly, but unless he is good at fuzzy logic system tuning he is much
>more likely to produce a system with hidden ugly bugs than with PID. I
>have mentioned servo play in a previous posting in this context, PID is
>fooled by this, fuzzy can do.
>
>Peter
>

I read a week or so ago that an Australian designed model aircraft
(intended for meteorological uses I think) has just crossed the
Atlantic Ocean under its own control. Wingspan was about 2 metres I
think.
.
.
-----Original Message-----
From: Peter L. Peres <EraseMEplpACTCOM.CO.IL>

>If you read between the lines, a small RC aircraft or boat can be
turned
>easily into a torpedo or cruise missile, with 1-4 kg of explosive on
>board. You DON'T want college kids playing with that, nor anything
like
>this available off the shelf to be bought by your next door
revolutionary
>cell techie.

> > At 18:55 24.9.1998 +0000, you wrote:
> > have you seen and/or used the miniature flux gate compass sold by
> > Jameco
> >for heli/model directional and heading control ? Have you considered it
> >for this ? (and is it legal in your country ? <g>).
> >
>
> I have two of those toys (Vector 2X or something.., the gimbaled ones). I
> am affraid that the whole thing is too weak to withstand the vibrations in
> any RC model, especially in heli. On the other side, I tried one compass
> with success in RC car.
>
> PavelK
>
Have you checked out these guys?http://idt.net/~aosi/

> OK Folks,
> So which one of the you guys is going to step forward to provide the fuzzy
> logic tutorial. I would love to try and get to grips with this maybe we
> could use this heli control system as an example.....
>
> Or at least maybe those in the know could provide a few good pointers to
> books/articles/Web pages etc.

Hrrmph,

ok, there is annabooks who have a title on Fuzzy Logic, with examples in C
(I haven't bought it so I don't know).

Now, for a crash course in 20 words:

Fuzzy logic is a generic name for closed or open loop control algorythms
that are capable to operate over a non-continuous target domain, as
opposed to PID and other algorythms.

A simple servo fuzzy logic system is implemented as a closed loop system
with an actuator, a sensor, an input value and a processor that operates
on the input values (sensor and control) to drive the actuator.

The processor implements a whole set of process equations, as opposed to
one for PID et al. At any given moment only one equation functions, but
the equation can be changed depending on the exact system parameters at
that point. A state machine in the processor keeps track of the current
state and changes the current equation depending on system parameters.

Fuzzy servos can handle such things as mechanical play in linkages,
unbalanced moving weights attached to a rotating target and other 'nice'
real world problems.

One can implement a fuzzy processor from scratch, knowing only this, but
usually templates or code generators are used. Books on Fuzzy contain
such coding templates and code generators.

> I read a week or so ago that an Australian designed model aircraft
> (intended for meteorological uses I think) has just crossed the
> Atlantic Ocean under its own control. Wingspan was about 2 metres I
> think.

I know about the Aerosonde project (I think thta this is the official name
for it), but I was talking about different aspects of the problem. I never
said it can't be done, I said, that it matters a lot who is doing it and
how detailed the leaked technology is.

At 18:04 25.9.1998 +0000, you wrote:
>On Fri, 25 Sep 1998, Pavel Korensky wrote:
>
>> P.S. Why it should not be legal to put compass,GPS,IR tracking device or
>> anything else into RC heli ?
>
>The last time I checked, adding auto-pilot features to any mobile such
>that it can navigate without human countrol makes it illegal as a model.
>There is also a weight limit for models that can be flown in most
>countries (USA == 5 kg ?).

We have no such limitations here. Except models used for competitions,
where weight limit is given by FAI. But AFAIK the 5 kg is not more a weight
limit for competition models in F4C (scale models) and F3A (R/C acrobats).

>
>If you read between the lines, a small RC aircraft or boat can be turned
>easily into a torpedo or cruise missile, with 1-4 kg of explosive on
>board. You DON'T want college kids playing with that, nor anything like
>this available off the shelf to be bought by your next door revolutionary
>cell techie.

It is not necessary to read between lines, I already saw too much R/C toys
with explosives in fancy Hollywood movies.
On the other side, I think that this kind of limitations is really stupid.
College kids have no access to off the shelf explosives (at least in my
country). If some kid is smart enough to develop and build auto-pilot
guided missile, I think that the same kid is smart enough to cook some
explosives. In this case, I am almost sure, that the kid is smart enough to
not to use it.

And if some real terrorist want to destroy anything, it is far less
complicated to buy real guided missile, either from black market gun dealer
or (better) directly from army. It is not joke, we had one case two years
ago. One guy bought the whole tank, directly from one army collonel. When
police got him, he had the tank in garage, fully loaded with ammo.

>
>At the present stage of things, it works out like this: better technology
>and systems are protected from public access by an IQ barrier, in the
>sense that you need to understand the technology in order to be able to
>use it. Look for example at good computing technology: you have to
>understand Unix to be able to use them. Otherwise you are stuck with GPFs
>and limited choice menus (but with rewarding animations) <g>.

At 15:03 25.9.1998 -0400, you wrote:
>Israel exports model auto-pilot systems for hobby use in the USA (see Hobby
>Lobby online). Many autonomous robots are built here for experimental
>non-military use. We regularly fly models over 5Kg here, also. 5Kg is a
>typical model weight (11 pounds or so).

Similar auto-pilots are available here. It is called HAL (Horizontal Auto
Leveling system). I recently bougt one of those instruments for R/C trainer
which my girlfriend is flying. I disassemble the box and it is clever
design. Atmel chip inside and four optical sensors. The Atmel is measuring
the level of light on sensors (forward, backward, left, right) and
adjusting servo pulses for elevator and ailerons.
It sounds funny and the whole thing was so cheap that I was not able to
believe that it can work. I tried it the model and it works like a charm.
Not only for flight stabilisation, but the aircraft behave like cruising
missile. You can fly two meter above the ground, directly into the trees.
Suddenly, at the distance around 10-20 meters before the trees, the
airplane starts to climb above the trees. On the other side, the plane is
not able to go back to the previous flight level when it is beyond the trees.
But it should not be too hard to mix the signal from HAL with some signal
from altimeter for flight level stabilisation. And also GPS or DGPS can be
added for enhanced functionality.

>Similar auto-pilots are available here. It is called HAL (Horizontal Auto
>Leveling system). I recently bougt one of those instruments for R/C trainer

Hobby Lobby (which imports a lot of Czech stuff to the USA) sells the HAL.
I was referring to the BTA autopilot, which is a true autopilot system
whereas HAL is a leveling device, designed to keep all directions in
(relatively) equal illumination.